Transmission of data packets over wired and wireless links needs to be fast and reliable. Speed requirements are set by seemingly ever-increasing data transfer rates, and quality of service requirements are set by increasing system needs for accuracy in transmissions.
Digital data transmissions over wired and wireless links sometimes may be corrupted, for instance, by noise in the link or channel, by interference from other transmissions (e.g., radio), or by environmental factors related to, for example, the speed, direction, location and requests between transmitting and receiving units. Even with clear communication channels (i.e., channels with limited corruption), which lend themselves to the high data rates, it may not be possible to appropriately decode the data stream with the requisite error rates. Digital data transmissions may also be limited by an inability of the receiving or transmitting equipment to appropriately encode and decode the data stream at the speeds desired with the requisite error rates.
It may be infeasible to provide hardware suitable for high rate data transmission at a cost and portability demanded by the application. Requested services may range from voice communications over high-speed Internet connections to video conferencing. The hardware at the receiver end should be light and small, and use minimal amounts of power. Similarly, digital signal processing hardware for accurate conveyance of data packets should be compact and consume low power. Portability restrictions may require that all system attributes be well designed, using a minimal amount of integrated circuits, electronic components, batteries, and other components.
Error detection and correction codes typically provide mechanisms necessary to reliably receive and decode data packets. Forward error correction (FEC) codes allow decoders to accurately reconstruct data packets received with possible errors at the expense of some additional overhead (e.g., extra parity bits, extra symbols). Forward error protection may protect a data packet. With FEC, the protected data packet is generally “self-decoding” in that all the data (information) required to reconstruct the data packet is within a single receive block. Stored data may rely on FEC for reliable extraction.
In two-way systems, an opportunity for requesting that a data packet be retransmitted upon detection of an error may be available. An automatic repeat request (ARQ) may be sent upon detection of an error using, for example, a parity bit check or a cyclic redundancy check (CRC), and then the original data packet may be discarded. Upon receipt of an ARQ request, the packet may simply be retransmitted in its original form.
This simple combination of ARQ and FEC is sometimes called Type I hybrid ARQ, and the term “hybrid ARQ” is usually reserved for a more complex procedure where a receiver may combine previously received erroneous packets with a newly received packet in an effort to successfully ascertain the contents of the packet. The general procedure in a hybrid automatic repeat request (HARQ) system is that a receiver may generate an indicator, such as an ARQ request, upon detection of an error in the received data packet. Unlike Type I ARQ, the receiver does not discard previously received erroneous packets. The receiver may keep (that is, store) the entire or portions of the erroneous packet because the erroneous packet may still contain worthwhile information, and therefore is not discarded when using HARQ. By combining erroneous packets, the receiver may be able to assist the FEC to correct the errors. The receiver may require, however, an abundance of volatile memory for storing previous data packets and provisioning for the needs of the HARQ decoder. A HARQ buffer may contain a large amount of memory designated for just this purpose. Large memory requirements, particularly in portable, mobile equipment, may require excessively large space and consume an excessively large amount of power. A method for decreasing the amount of memory required for a HARQ system is therefore desirable. Methods for managing and optimizing volatile memory available in a communication system are also desirable. The method should be compatible with any ARQ protocol, such as selective-repeat or multi-channel stop-and-wait, and capable of being used with all underlying types of HARQ.
It is desirable to have a system and method of efficiently storing HARQ data packets. It is desirable that the system and method allow for storage of the HARQ data packets in more compact, less-power consuming memory that is presently available.